As compared to the cathode ray tube (CRT), the liquid crystal display apparatus is enlarged in display size, lighter in weight and lower in power usage, so that it is used for a television receiver or for a variety of display devices, as is a self-light-emitting PDP (plasma display panel), as an example. The liquid crystal display device encloses liquid crystal between two transparent substrates of variable sizes and applies electrical voltage across two electrodes provided to the transparent substrates to change the orientation of the liquid crystal molecules and light transmittivity to make optical display of, for example a preset image.
In the liquid crystal display device, the liquid crystal itself is not light radiating, and hence a light source is provided for causing illuminated light to be incident on the liquid crystal panel. The light source used may be of the side light system in which illuminating light is incident from a lateral side of the back surface of the liquid crystal panel, or of the back light system in which illuminating light is directly incident from the back side of the liquid crystal panel. The backlight unit, configured for supplying the illuminating light from the back side of the liquid crystal panel, includes a light source, a light guide plate guiding the illuminating light radiated from the light source to the liquid crystal panel, a reflective sheet, and a lens sheet or a light diffusing sheet, and is configured for causing the illuminating light, radiated from the light source, to be incident on the entire surface of the panel.
As a light source, used for this sort of the backlight unit, a cold cathode fluorescent lamp (CCLF), having mercury or xenon enclosed in a fluorescent tube, is used. This type of the backlight unit has such defects that it is low in light emitting brightness of the cold cathode fluorescent lamp and is of short useful life, and that a low brightness area may be present on the cathode side such that uniform brightness cannot be maintained.
In a liquid crystal display apparatus of a large display size, an area lit configuration backlight device, provided with plural elongated cold cathode fluorescent lamps on the back surface of a light diffusing plate, is used for illuminating display light on the liquid crystal panel. This area lit configuration backlight device also suffers the problem ascribable to the cold cathode fluorescent lamp and, if the device is used for a large format television receiver, exceeding 30 inches, the problem of insufficient brightness or insufficient uniformity of brightness becomes more prominent.
On the other hand, in the area lit configuration backlight device, there has been proposed an LED area lit configuration backlight, in which larger numbers of light emitting diodes, sometimes abbreviated to LEDs, of three prime colors, namely red, green and blue light emitting diodes, are arrayed two-dimensionally on the back surface side of the light diffusing film to obtain white light. In LED area lit configuration, it is possible to accomplish picture display to high brightness on a large-sized liquid crystal panel with a low power usage at a reduced cost of the LEDs.
Meanwhile, as a light source used for an LED backlight device, there have so far been provided a large number of the LEDs arrayed in a matrix configuration or in an array configuration. In the array configuration LED backlight device, a large number of LEDs are mounted on the same co-axial line on an interconnection substrate to form a light emitting unit, whilst a plural number of the light emitting units are arrayed on the same co-axial line to form a light emitting array and a plural number of such light emitting arrays are arranged at an equal interval from one another to form a light emitting system. If, in this LED backlight device, a large volume of illuminating light, radiated from many LEDs, is directly incident on the liquid crystal panel through a light guide plate, color irregularities or lamp image are sometimes produced on the liquid crystal panel.
Thus, in the LED backlight device, a light diffusing plate is arranged between a light guide plate and the light emitting unit, the light radiated from each LED is prohibited from directly falling on its area facing each LED, that is, the light is once reflected or controlled in the incidence volume and transmitted through its peripheral area. Also, in the LED backlight device, a so-called side emission LED having directivity such as radiates the outgoing light mainly towards the outer periphery, is used as each LED, in such a manner that the light radiated from each LED will be incident on a peripheral area of the light diffusing plate, by way of light equalization.
With the LED backlight device, a reflecting plate is combined with each light emitting unit so that illuminating light will be efficiently incident on the liquid crystal panel. Moreover, with the LED backlight device, the outgoing light, reflected by the light diffusing plate, or the outgoing light radiated towards the outer rim, is reflected by the reflecting plate to fall on the light diffusing plate. The reflecting plate is formed with many guide through-holes in register with the respective LEDs, and the light emitting parts of the LED units are protruded towards the liquid crystal panel through these guide through-holes.
Meanwhile, in the conventional LED backlight devices, polymer-coated reflective plates are used as substrates formed as expandable PET (polyethylene terephthalate) or aluminum plate. The reflective plate is formed to substantially the same shape as the liquid crystal panel. In addition, in the conventional LED backlight devices, a hermetically sealed spatial section is provided on the back side of the liquid crystal panel for prohibiting leakage of the illuminating light to outside. In this spatial section, there are arranged the aforementioned large number of the LEDs and plates. In this configuration of the LED backlight device, there is accumulated heat generated in the LEDs. If heat is evolved in the LED backlight device, the optical components or the reflective plate, making up the device, are expanded and changed in size, with the result that relative position accuracy between each LED unit and the guide through-holes formed in the reflective plate is subjected to offset.
Moreover, with the above-described LED backlight device, having the above-described structure of the light emitting array, the relative positioning variations in the dimensional accuracy of the interconnection substrate, mounting accuracy of the LEDs, dimensional accuracy of the back panel and in the assembling accuracy of the reflective plate significantly affect the accuracy in relative positions between the LEDs and respective guide through-holes provided in the reflective plate engaged by these LEDs. The LED backlight device is loaded with an increasing number of LEDs, while the reflective plate is increased in size, with increase in the size of the liquid crystal panel. In addition, there are provided a large number of guide through-holes corresponding to the number of the LEDs.
Meanwhile, with the conventional LED backlight device, the machining accuracy of the respective components is made higher, while the components are assembled to high accuracy, to suppress the adverse effects of the positioning offset otherwise caused due to heat generation between the large number of the LEDs and the respective guide through-holes provided in the reflective plate and which are engaged by these LEDs.
However, if the machining accuracy as well as assembling accuracy of the components is made higher, not only is the production cost raised, but also the production efficiency is deteriorated.
The guide through-holes, provided in the reflective plate, are larger in diameter than the LED size in order to take up the position offset between the guide through-holes and the LEDs engaged therein. Should the guide through-holes be enlarged in diameter in this manner, a large gap is produced between the guide through-holes and the LEDs, engaging therewith, so that the illuminating light is leaked through the gap to the back side to lower the light utilization efficiency. Moreover, it becomes necessary to take measures for shielding the light leaked to the back side, thus leading to a complicated structure.
The reflecting plate needs to be of a size matched to the size of the LED backlight device. If the LED backlight device is increased in size, the reflecting plate itself also is to be increased in size. For producing a large-sized reflective plate, it has to be prepared from a material having a sufficient mechanical rigidity. So, the reflective plate formed by an aluminum plate is used. The aluminum plate, forming the reflecting plate, has its surface coated with a polymer, as an insulating material, for assuring electrical insulation. Even if the surface of the aluminum plate is coated with the insulating material, but if guide through-holes engaged by the LEDs are then formed, the aluminum base material is exposed on the inner peripheral surfaces of the guide through-holes, such that there is a risk that electrical insulation cannot be maintained between the reflective plate and the terminal part of the LED, engaged therewith. For resolving this problem, it is contemplated to enlarge the guide through-hole so as to be larger than the outer size of the LED to prevent the terminal of the LED from contacting with the inner surface of the guide through-hole. However, if the guide through-hole is increased in size, the gap between it and the LED part, engaged therewith, is also increased to increase further the leakage of the illuminated light to the back side.
Problem to be Solved by the Invention
It is an object of the present invention to provide a backlight device and a liquid crystal display apparatus whereby the above problem may be overcome and the utilization efficiency of light radiated from a light source is improved to enable light picture display.
It is another object of the present invention to provide a backlight device and a liquid crystal display apparatus whereby leakage of light radiated from the light guide spatial section is suppressed to improve the light utilization efficiency as the machining and assembling of respective component parts are facilitated.
In a backlight device according to the present invention, many light emitting diodes are mounted on the same axis on one surface of an interconnection substrate to form a light emitting unit, and a plurality of such light emitting units are arrayed at equal intervals on the same co-axial lines through an optical sheet block to form a light emitting array on which falls the illuminated light. This backlight device includes plural numbers of reflective sheet pieces and reflective plates which are assembled to a heat radiating plate carrying plural interconnection substrates and forming the light emitting array.
A heat dissipating plate is formed of a metal material having heat conductivity, in which the major surface of a base thereof is formed with a substrate fitting part for carrying the interconnection substrates side-by-side along both sides of the substrate fitting part. There are formed reflective plate supports for extending along both lateral sides of the substrate fitting part. The respective reflecting sheet pieces are formed of a sheet material exhibiting reflection characteristics and are of a length corresponding to the length of a preset number of light emitting diodes and a width smaller than the width of the heat radiating plate. Each of the reflective sheet pieces includes a plurality of guide through-holes through which are passed light emitting parts of the light emitting diodes. The reflecting plate is formed from a plate material exhibiting reflective characteristics to an outer shape approximately equal to the outer shape of the liquid crystal panel. The reflecting plate has a plurality of rows of guide openings through which are passed the light emitting parts of the light emitting diodes.
The reflecting sheet pieces are mounted to the heat radiating plates as the light emitting parts of the light emitting diodes are protruded via facing guide through-holes, with the reflecting plate being superposed on the reflective sheet pieces and bonded in this state to the reflective plate supports of the heat radiating plate, in a manner that the light emitting diodes protruded through the guide through-holes of the reflective sheet pieces are protruded through the guide openings to face the back side of the liquid crystal panel. The reflecting plate, bonded to the heat radiating plate, holds each reflecting sheet pieces to prevent the outgoing light radiated from the light emitting diodes from leaking to the back surface side.
With the backlight device, according to the present invention, in which the reflective sheet pieces are assembled from one light emitting unit to another, the light emanated from the light emitting diodes may be prevented from leaking via the guide through-hole without it being necessary to assure excessive accuracy in machining and assembling the light emitting diodes engaged in these guide through-holes.
A heat pipe fitting part is formed in the base of each heat radiating plate, over the entire longitudinal length of the base. A heat pipe is mounted in the heat pipe fitting part in close contact with its inner wall and heat generated from the light emitting diodes and conducted to the heat dissipating plate is transmitted to heat dissipating means by the heat pipe assembled in the heat pipe fitting part.
A dust-proofing elastic member is bonded to each reflective plate support provided on a lateral side of each heat radiating plate. Each dust-proofing elastic member closes the opened lateral side of the substrate fitting part, carrying the interconnection substrate, for preventing dust and dirt from intruding into the inside of the substrate fitting part.
Each guide opening formed in the reflective plate in association with each light emitting array is formed by a number of groups of guide openings arranged on the same coaxial line, with each group being separated from each neighboring group by a bridge for allowing a plurality of the light emitting diodes to pass therethrough.
The reflecting sheet pieces are assembled to the respective interconnection substrates as the light emitting diodes are passed through the guide through-holes. The reflecting plate is mounted to the reflecting plate supports of each heat radiating plate. Each bridge of the reflecting plate thrusts the reflecting sheet pieces against the heat radiating plate to prevent floating of the reflecting sheet pieces.
Each reflecting sheet piece is formed by an insulating polymer sheet material, and the reflecting plate is formed from an aluminum substrate. To the inner peripheral edge of each guide opening, faced by the aluminum substrate, forming the reflective plate, is mounted an inner peripheral edge of each guide through-hole formed in each reflective sheet piece lesser in diameter than the guide opening over the entire periphery. By the portion of each reflective sheet piece protruding towards the inner peripheral edge of each guide opening of the reflective plate, it is possible to maintain electrical insulation between the aluminum substrate forming the reflective plate and the terminal part of each light emitting diode by each reflective sheet piece.
A liquid crystal display apparatus according to the present invention includes a light transmitting liquid crystal panel, a backlight section having a large number of light emitting diodes for causing a large volume of illuminating light corresponding to the light radiated from the light emitting diodes to the liquid crystal panel, an optical converting section for subjecting the illuminating light to preset optical conversion and for causing the resulting illuminating light to fall on a liquid crystal panel, a light guide unit for causing the illuminating light to fall in an equalized state on the liquid crystal panel, a reflecting part for reflecting the light radiated from each light emitting diode to the surrounding towards the light guide unit, and a heat dissipating section for dissipating the heat generated in the backlight section. The backlight section includes a plurality of light emitting arrays arranged at equal intervals on one surface of an interconnection substrate, each light emitting array being composed of a plurality of light emitting units, each of which is made up of a plurality of light emitting diodes mounted on the same co-axial line. The optical converting section is arranged between the liquid crystal panel and the backlight section, and formed by a laminate of a plurality of functional optical sheets for processing the illuminating light supplied from the backlight section with preset optical conversion to send the so converted illuminating light in a stabilized state to the liquid crystal panel. The optical converting section is formed by a laminate of functional optical sheets, arranged between the liquid crystal panel and the backlight section, and performs the role of polarizing the illuminating light to orthogonal components, the function of correcting the phase difference thereof to widen the angle of field of view and to prevent coloration, and the function of light diffusion, thereby allowing the illuminating light, radiated from the backlight section, to fall in a stabilized state on the liquid crystal panel.
The light conducting section includes a light diffusing light guide plate and a light diffusing plate. The light diffusing light guide plate is formed from e.g. a milk-white light conducting polymer material to a veritable thickness and diffuses the incident illuminating light in the inside thereof to emit the resulting light from the entire surface thereof in an averaged state to the optical converting section. The light diffusing part of the light conducting section selectively performs the reflective diffusing operation and light transmitting operation on the illuminating light to equalize the luminance to cause the light to be incident on the light diffusing light guide plate. The light diffusing plate is formed e.g. of a transparent polymer material and many light dimmer parts exhibiting light reflecting diffusing properties are formed in the portions thereof in register with the respective light emitting diodes. The light diffusing plate controls the volume of light radiated from the directly underlying light emitting diodes and incident thereon to suppress generation of a partially high brightness area to permit the backlight to be incident on the entire surface of the light diffusing light guide plate with even brightness.
The heat radiating section is formed of a metal material exhibiting heat conductivity and includes, on the major surface of a base, a plural number of heat dissipating plates, each having a substrate fitting part, supporting plural interconnection substrates side-by-side along the longitudinal direction on the same co-axial line. The heat radiating plates form support members of the light emitting units and represent heat dissipating plates associated with a plural number of light emitting arrays by being arrayed co-axially at equal intervals one from another on the back surface of the liquid crystal panel. Each heat dissipating plate includes upstanding reflective plate supports for extending along both sides of the substrate fitting part and the reflecting plate is bonded to these reflective plate supports.
Each heat dissipating plate is provided with a plural number of groove-like heat pipe fitting parts, in a bottom surface section of the base formed with substrate fitting sections, with each of heat pipe fitting parts being composed of plural heat pipe fitting parts arranged side-by-side along their entire lengths on the same co-axial line. A heat pipe is assembled in the heat pipe fitting part of each heat radiating plate in tight contact with the inner wall thereof and heat evolved in the light emitting diodes is transmitted by this heat pipe to a heat dissipating means.
The reflecting section reflects the light radiated from each light emitting diode to the surrounding and the light reflected from a light dimmer part of the light diffusing plate towards the light guide section. This reflecting section includes a plurality of reflective sheet pieces and a reflecting plate having an outer shape approximately equal to that of the liquid crystal panel. Each of the reflective sheet pieces is formed from a sheet having reflecting properties to the shape of a rectangle having a length corresponding to a preset number of the light emitting diodes and a width smaller than the width of the heat radiating plate. Each reflective sheet piece is provided with a large number of guide through-holes formed on the same axial line. These guide through-holes are provided for extending along the same co-axial line and are passed through by light emitting parts of the light emitting diodes.
The reflecting sheet pieces are mounted to the heat dissipating plate as the light emitting parts of the light emitting diodes are protruded through the guide through-holes facing the light emitting parts. The reflecting plate is bonded to the reflecting plate supports of the heat radiating plates as the reflective plate is superposed on the reflective sheet pieces to form the reflective section. The light emitting diodes protruded from respective guide through-holes of the reflective sheet pieces face the back surface section of the liquid crystal panel as the respective light emitting parts are protruded from the guide openings.
The heat generated in the plural light emitting diodes is dissipated through a heat dissipating plate having the function of supporting the interconnection substrate. The heat pipe is assembled in the heat pipe fitting part, formed over the entire area along the length of the bottom surface of the base of the heat dissipating plate, in tight contact with the inner wall thereof, for transmitting the heat evolved in each light emitting diode and transmitted to heat radiating means.
The guide opening formed in the reflective plate in association with each light emitting array is formed by a plural number of groups of guide openings arranged on the same coaxial line, with each group of guide openings being separated from a neighboring group by a bridge for allowing a plurality of the light emitting diodes to pass therethrough. As the reflecting plate is bonded to the reflecting plate supports of each heat radiating plate, the bridge thrusts the reflective sheet pieces towards the heat radiating plate to hold the reflective sheet pieces against floating.
The reflective sheet pieces are formed of an insulating polymer sheet material, whilst the reflective plate is formed of aluminum as base material. An opening edge of each guide opening in the reflective sheet piece is protruded inwards over an entire peripheral part from an opening edge of each guide through-hole of the reflective sheet piece, smaller in diameter than each guide opening, in a manner of maintaining electrical insulation between the inner edge of each guide opening and a terminal part of each light emitting diode.
With the backlight device and the liquid crystal display apparatus, employing the backlight device, according to the present invention, picture display may be made to high brightness, even in a large sized liquid crystal panel, as a large volume of illuminating light is supplied from the back panel in an equalized state. Even in case high machining accuracy or high assembling accuracy of the component parts is not maintained, the illuminating light radiated from each light emitting diode may be suppressed from leakage to improve light utilization efficiency to enable display to high brightness.
Other objects and specified advantages of the present invention will become more apparent from the following explanation of preferred embodiments thereof especially when read in conjunction with the drawings.